<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>

    <style>
        .a{
            width: 400px;
            height:400px;
            display: flex;
            background-color: red;
            justify-content: center;
            align-items: center;       
        }
        .b{
            width: 100px;
            height:100px;
            background-color: yellow;
            
        }
    </style>
</head>

<div class="a">
    <div class="b"></div>
</div>

<body>
    <script>
       let n=3.1415;
       console.log(Math.ceil(n));
       console.log(Math.floor(n));
       console.log(n.toFixed(2));
       
    </script>
</body>
</html>